The invention relates to the field of photorefractive crystal material.
Three-dimensional optical storage will enter the market, but it does not mean that the product has been done very well. The main problem is no excellent three-dimensional optical storage material found. In fact, scientists in the world have been looking for satisfied three-dimensional optical storage material for a long time. Up to now, the iron doped lithium niobate is still considered as the first candidate. But there are big shortcomings for LiNbO3:Fe, such as a too long response time and a low ability to resist optic scattering (A. Hellemans, Holograms can storage terabytes, but where? Science 286 (1999) 1502). Now, improving and optimizing the properties of LiNbO3:Fe crystal (restrain the laser induced voltage effect and maintain its good photorefraction properties in the mean time) is still the most important task at present.
The objection of this invention is to supply a doubly doped lithium niobate crystal, which is an improvement and optimization of LiNbO3:Fe, and has an excellent photorefractive properties, and can be used as the three-dimensional holographic optical storage material.
The doubly doped lithium niobate crystal of the invention is doped with iron and a second radius-matched metal ion in the meantime. Its composition can be denoted as Li1xe2x88x92xNb1+yO3:Fem,Mn, where M is magnesium, indium, or zinc; when using q to denote the ion valence of M (q=2 when M is Mg or Zn, and q=3 when M is In), the values of x, y, m, and n are in the range of 0.05xe2x89xa6xxe2x89xa60.13, 0.00xe2x89xa6yxe2x89xa60.01, 5.0xc3x9710xe2x88x925xe2x89xa6mxe2x89xa67.5xc3x9710xe2x88x924, and 0.02xe2x89xa6qnxe2x89xa60.13, respectively.
The composition of doubly doped lithium niobate crystals can:
doped with 0.007xcx9c0.03 wt. % Fe and 1.0xcx9c5.0 mol. % Mg,
doped with 0.01xcx9c0.05 wt. % Fe and 0.75xcx9c3.0 mol. % In, or
doped with 0.02xcx9c0.06 wt. % Fe and 1.5xcx9c6.5 mol. % Zn,
While the congruent composition is [Li]/[Nb]=0.87xcx9c0.95.
The implement steps of the invention are:
(1) Weigh up Li2CO3, Nb2O3, Fe2O3, and MgO, In2O3 or ZnO powders according to the crystal composition, and dry them at 120xcx9c150xc2x0 C. for 25 hours, then thoroughly mix them at a mixer lasting for 24 hours, and keep them at 800xcx9c850xc2x0 C. for 2xcx9c5 hours to make Li2CO3 decompose sufficiently, and then sinter at 1050xcx9c1150xc2x0 C. for 2xcx9c8 hours to obtain doubly doped lithium niobate powder. (2) Put the above doped lithium niobate powder into a Pt crucible after impacted then heat the powder by a middle frequency stove. Grow the doubly doped lithium niobate crystals using the Czochralski pulling method along c or a axis via the procedures of necking, shouldering, uniform-diametering, and tailing, with the pulling rate being 1xcx9c3 mm/h, the rotation rate being 15xcx9c30 rpm, the temperature difference of the melt-crystal interface being 20xc2x0 C., the temperature gradient in the melt volume near the surface being 1.5xc2x0 C./mm, and the temperature gradient above the melt surface being 1.0xc2x0 C./mm, respectively. (3) Pole and anneal the grown doped lithium niobate crystals at 1200xc2x0 C. to obtain a single-domain structure.